The key to the Senate Gang of Six deficit-cutting grand bargain is the combination of higher tax revenue with lower tax rates.

The former makes Democrats swoon and Republicans are sweet on the latter.

The first date was a hit, with a surprising number of senators declaring their everlasting love and President Obama giving it his blessing on Tuesday. But just how much do the two sides know about their partner?

The Gang of Six maintained an aura of mystery. Its initial five-page summary left key details unstated and created some misimpressions, but offered enough clues to provide some clarity.

Here is a look at some elements of the emerging tax deal:

The deal would raise roughly $2 trillion in revenue over a decade relative to current policy, according to the House Budget Committee. That includes $1.2 trillion in revenue acknowledged by the Gang of Six. The rest comes from letting the Bush tax cuts expire for upper-income households.

While marginal taxes would fall for many, tax rates on capital gains and dividends would increase.

Based on estimates by the 2010 White House Fiscal Commission, whose plan the Gang of Six is modeled on, revenue would slightly top 20% of GDP.

That would be just shy of a record and up from the long-term average of 18.5%. The current take is near 15% of GDP, mainly due to the weak economy.

The added revenue would be raised by curbing so-called tax expenditures — a variety of credits, deductions and exclusions — even as the hated alternative minimum tax is eliminated and marginal income-tax rates are cut.

Much like the tax reform plan developed by the Fiscal Commission, the Gang of Six plan would condense the current five income-tax brackets into three.

The top two brackets (33% and 35%) would be condensed into a single rate between 23% and 29%, the Gang of Six said. But additional details suggest that the rate would be near the upper end of that range, said Donald Marron, director of the Urban-Brookings Tax Policy Center.

That's because the 23% rate option in the fiscal commission's report was tied to eliminating all tax expenditures. The Gang of Six plan stresses that it would "reform, not eliminate, tax expenditures for health, charitable giving, homeownership and retirement, and retain support for low-income workers and families."

Ganging Up On Investment

Among the words and phrases that didn't make it into the Gang of Six outline are long-term capital gains and dividends, which would be subject to much higher rates. Such income is now taxed at a top 15% rate following the 2003 tax cuts, but Gang of Six member Sen. Tom Coburn, R-Okla., told CNBC that capital gains would be subject to a 20% rate

The key to the Senate Gang of Six deficit-cutting grand bargain is the combination of higher tax revenue with lower tax rates.

The former makes Democrats swoon and Republicans are sweet on the latter.

The first date was a hit, with a surprising number of senators declaring their everlasting love and President Obama giving it his blessing on Tuesday. But just how much do the two sides know about their partner?

The Gang of Six maintained an aura of mystery. Its initial five-page summary left key details unstated and created some misimpressions, but offered enough clues to provide some clarity.

Here is a look at some elements of the emerging tax deal:

The deal would raise roughly $2 trillion in revenue over a decade relative to current policy, according to the House Budget Committee. That includes $1.2 trillion in revenue acknowledged by the Gang of Six. The rest comes from letting the Bush tax cuts expire for upper-income households.

While marginal taxes would fall for many, tax rates on capital gains and dividends would increase.

Based on estimates by the 2010 White House Fiscal Commission, whose plan the Gang of Six is modeled on, revenue would slightly top 20% of GDP.

That would be just shy of a record and up from the long-term average of 18.5%. The current take is near 15% of GDP, mainly due to the weak economy.

The added revenue would be raised by curbing so-called tax expenditures — a variety of credits, deductions and exclusions — even as the hated alternative minimum tax is eliminated and marginal income-tax rates are cut.

Much like the tax reform plan developed by the Fiscal Commission, the Gang of Six plan would condense the current five income-tax brackets into three.

The top two brackets (33% and 35%) would be condensed into a single rate between 23% and 29%, the Gang of Six said. But additional details suggest that the rate would be near the upper end of that range, said Donald Marron, director of the Urban-Brookings Tax Policy Center.

That's because the 23% rate option in the fiscal commission's report was tied to eliminating all tax expenditures. The Gang of Six plan stresses that it would "reform, not eliminate, tax expenditures for health, charitable giving, homeownership and retirement, and retain support for low-income workers and families."

Ganging Up On Investment

Among the words and phrases that didn't make it into the Gang of Six outline are long-term capital gains and dividends, which would be subject to much higher rates. Such income is now taxed at a top 15% rate following the 2003 tax cuts, but Gang of Six member Sen. Tom Coburn, R-Okla., told CNBC that capital gains would be subject to a 20% rate

The Fiscal Commission treated investment income as ordinary income. The Gang of
Six may have opted to keep some preference for investment income while not
reducing the top marginal income tax rate by as much..

That top rate doesn't include the Medicare tax passed along with the Affordable Care Act (a.k.a. ObamaCare). The act put a 3.8% tax on nonwage income, such as capital gains, starting in 2013. Thus, the top rate on capital gains and dividends could rise to 23.8%, a 59% increase from current levels.

While the corporate tax rate would be lowered from 35% to a maximum 29%, such cuts would come while eliminating loopholes to avoid any revenue loss.

Marron said he'd like to see a full analysis of the plan's impact on investment to better gauge the impact of the higher capital gains and dividend tax rates.

Two of the most costly tax subsidies that would be reformed are the mortgage interest deduction and the tax exclusion for employer-provided health benefits.

While the Gang of Six didn't get into the details, the fiscal commission offers a clue. That plan would cap the mortgage interest deduction to loans up to $500,000 and be turned into a flat 12% tax credit.

The tax-free status of employer-provided care would be capped in 2014 and gradually phased out.

That step would have a side-effect whose fiscal impact hasn't been scored: More and more people would shift from employer coverage to the new taxpayer-subsidized ObamaCare exchanges.

Upper-Middle Squeeze

While the real draw of this bargain is lower marginal rates, there's a good chance that they would actually rise for some members of the upper-middle class.

That's because the fate of the Gang of Six plan is tied to enactment of Social Security reform. The fiscal commission's Social Security plan, a likely model, gradually raised the $106,800 in wage income subject to the 12.4% payroll tax.

If the Gang of Six plan followed the same course, some taxpayers now in the 28% bracket would face a rate of about 34%.

Raising more revenue while getting rid of "garbage in the tax code" and lowering rates, is sensible, in theory, said economist Kevin Hassett of the free-market American Enterprise Institute.

But, Hassett said the size of government has already increased enormously and he perceives "a tendency for spending to stick and for tax cuts to go away."

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